Unmanned vehicles have heretofore been guided through a warehouse or other storage facility by guidewire control systems. In addition, many manned material handling vehicles (such as forklifts, reach-trucks and order-pickers) can be alternatively controlled by a wire guidance system. Such additional control is a valuable operative feature.
The use of pairs of coils disposed on the vehicle centerline, in order to generate an error signal indicative of vehicle deviation from the embedded or buried wire, is also well known, as illustrated in U.S. Pat. No. 4,307,329 (issued to Taylor on Dec. 22, 1981).
U.S. Pat. No. 3,993,156 (issued to Rubel on Nov. 23, 1976), discussed in greater detail hereinbelow, discloses a pair of main coils arranged with their axes horizontally located between the wheels of a vehicle.
Designing a manned vehicle for wire guidance operations continues to pose several problems. Each warehouse facility that has installed guidewire controls for guided vehicles operates the controls at different wire frequencies and amplitudes that are designed for its own distinct wireguided system. Any mass-produced (non-customized) material handling vehicle must, therefore, have the capability of detecting (acquiring), recognizing and responding to the different frequencies and amplitudes of warehouse wire guidance systems.
It would be advantageous to provide one or more antennae capable of acquiring guidewire signals under adverse conditions.
It would also be advantageous to provide an antennae system capable of linearizing response over a relatively great distance.
It would also be advantageous to provide an antennae system that could correct automatically for varying signal levels (i.e., that could provide automatic gain control), and that could also adapt to a large range of signal levels from the guidewire.